如何在Swift中为NSLayoutConstraint设置动画？ [英] How do I animate a NSLayoutConstraint in Swift?

问题描述

我的目标是为 UIImageView 设置动画。我在 viewDidLoad 中声明了 NSLayoutConstraint 。在 viewDidLoad中中，我使用这个代码：

My goal is to animate a UIImageView. I declared a NSLayoutConstraint in viewDidLoad. In viewDidLoad, I used this code:

UIView.animateWithDuration(1, animations: {
    myConstraint.constant = 100
    self.view.layoutIfNeeded()
}, completion: {finished in })

为什么我的图像不移动？

Why doesn't my image move?

推荐答案

按点击 viewDidLoad 的时间，尚未应用约束引擎，并且尚未建立视图的起始位置。因此，随意添加在 viewDidLoad中原来的限制，但你会希望稍后推迟 animateWithDuration 直到过程（例如 viewDidAppear ）。

By the time you hit viewDidLoad, the constraints engine has not yet been applied and the starting location of the views has not yet been established. So, feel free to add the original constraints in viewDidLoad, but you will want to defer the animateWithDuration until later in the process (e.g. viewDidAppear).

例如，让我们假设您在Interface Builder（IB）中添加了一些约束。您可以通过 control 添加 @IBOutlet 引用 - 从Interface Builder左侧面板中的文档大纲中的约束拖拽到助理编辑：

For example, let's assume you have some constraint that you added in Interface Builder (IB). You can add an@IBOutlet reference to it by control-dragging from the constraint in the document outline in the left panel in Interface Builder down to the assistant editor:

现在您有参考对于该约束，您现在可以以编程方式更改该约束的常量值（但是，再次在 viewDidAppear 中执行此操作，而不是 viewDidLoad ，如果你想在视图出现时看到这个动画）：

Now that you have a reference to that constraint, you can now programmatically alter the constant value for that constraint (but, again, do this in viewDidAppear, not viewDidLoad, if you want to see this animated when the view is presented):

@IBOutlet weak var topConstraint: NSLayoutConstraint!

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)

    topConstraint.constant = 100
    UIView.animateWithDuration(2.0) {
        self.view.layoutIfNeeded()
    }
}

对于以编程方式创建的约束，该过程是相同的。只需保存对约束的引用，然后在 viewDidAppear 中更新常量，然后将调用设置为<$ c $。 c> layoutIfNeeded（）。

The process is the same for programmatically created constraints. Just save a reference to the constraint and then in viewDidAppear update the constant and then animate the call to layoutIfNeeded().

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